useEffect must not return anything beside a function, which is used for clean-up Error Comes up Every Screen

Question

I was trying the useEffect example something like below:

const navigation = () => {
const [isLogin, setLodin] = useState(undefined)

useEffect( async () => {
const username = await AsyncStorage.getItem('username')
if(username){
  setLodin(true)
  console.log(username)
}else{
  setLodin(false)
}

},[])

if (isLogin === undefined){
return (
  <View style={{flex:1, justifyContent: 'center', alignItems: 'center'}}>
    <ActivityIndicator />
  </View>
)

}

return (
<NavigationContainer>
  <Stack.Navigator screenOptions={{headerShown: false}}>
    {
      isLogin ? (
        <Stack.Screen
        name="HomeBtmTabNavigation"
        component={HomeBtmTabNavigation}
        />
      ) : (
    <>
      <Stack.Screen name="LandingScreen2" component={LandingScreen2} />
      <Stack.Screen name="LoginScreen" component={LoginScreen} />
      <Stack.Screen name="SignUpScreen" component={SignUpScreen} />
      <Stack.Screen name="SignUpSuccScreen1" component={SignUpSuccScreen1} />
      <Stack.Screen name="SignUpSuccScreen2" component={SignUpSuccScreen2} />
    </>
      )
    }
  </Stack.Navigator>
</NavigationContainer>

); };

But Warning Comes Up's: useEffect must not return anything beside a function, which is used for clean-up Error Comes up Every Screen.